mp4 files that are imported into Premier Elements 2026 either play poorly (stutter, etc) or not at all.

These mp4 files have excellent integrity on the brand new Windows 11 pc.  When I try to import them into Premier Elements 2026, they either do not play at all or play so poorly (extreme lags or stutters)  that I give up.  Adobe says this is an supported format and it should be because it is so prevalent. What gives?